﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MyConsoleApp.Code
{
    /// <summary>
    /// 集合所有排列
    /// var c1 = new string[] { "L", "Z", "G", "H" };
    /// SetAlgorithms.Arrangement(c1.Length, 3, (result, len) => {
    ///    Console.WriteLine("{0}{1}{2}", c1[result[0]], c1[result[1]], c1[result[2]]);
    ///    return true;
    /// });
    /// </summary>
    public static class SetAlgorithms
    {
        public delegate bool SetAlgorithmCallback(int[] result, int length);

        static bool CheckNM(int n, int m)
        {
            if (m > n || m < 0 || n < 0)
            {
                throw new ArgumentException();
            }

            if (m == 0 || n == 0)
                return false;
            return true;
        }

        static bool Arrangement(int n, int rlen, int[] result, SetAlgorithmCallback callback)
        {
            if (rlen == result.Length)
                return callback(result, rlen);

            for (int i = 0; i < n; ++i)
            {
                bool skip = false;
                for (int j = 0; j < rlen; ++j)
                {
                    if (result[j] == i)
                    {
                        skip = true;
                        break;
                    }
                }

                if (skip) continue;

                result[rlen] = i;

                if (!Arrangement(n, rlen + 1, result, callback))
                    return false;
            }

            return true;
        }

        public static void Arrangement(int n, int m, SetAlgorithmCallback callback)
        {
            if (!CheckNM(n, m)) return;

            var result = new int[m];
            for (int i = 0; i < n; ++i)
            {
                result[0] = i;
                if (!Arrangement(n, 1, result, callback))
                    return;
            }
        }
    }
}
